High energy density battery having unsaturated heterocyclic solvent containing electrolyte

ABSTRACT

HIGH ENERGY DENSITY GALVANIC BATTERIES HAVING HIGH UTILIZATION OF ACTIVE ELECTRODE MATERIAL WITH LOW GAS PRODUCTION CAN BE PREPARED USING VOLTIC CELLS HAVING AN ANODE OF ONE OF THE LIGHT METALS OF GROUPS I-A OR II-A OF THE PERIODIC TABLE, A COMPATIBLE METAL CATHODE AND AN ELECTROLYTE CONTAINING A SOLVENT COMPONENT CONSISTING ESSENTIALLY OF A MIXTURE OF FROM 5 TO ABOUT 80% BY WEIGHT OF A FIVE MEMBERED UNSATURATED HETEROCYCLIC HYDRACARBON COUMPOUND AND COMPLEMENTALLY FROM 95 TO ABOUT 20% BY WEIGHT OF A SATURATED ETHER AND A DISSOLVED SALT HAVING THE FORMULAS MM&#39;&#39;F6, MSCN OR MCLO4 WHERE M IS LI, NA, OR K AND M&#39;&#39; IS P, AS OR SB.

United States Patent O 3,778,310 HIGH ENERGY DENSITY BATTERY HAVINGUNSATURATED HETEROCYCLIC SOLVENT CONTAINING ELECTROLYTE Bruce HollisGarth, Newark, DeL, assignor to E. I. tlu Pont rle Nemours and Company,Wilmington, Del. No Drawing. Continuation-impart of abandonedapplication Ser. No. 112,415, Feb. 3, 1971. This application May 1,1972, Ser. No. 249,049

Int. Cl. H01m 11/00 US. Cl. 136-100 R 9 Claims ABSTRACT OF THEDISCLOSURE High energy density galvanic batteries having highutilization of active electrode material with low gas production can beprepared using voltaic cells having an anode of one of the light metalsof Groups I-A or ll-A of the Periodic Table, a compatible metal cathodeand an electrolyte containing a solvent component consisting essentiallyof a mixture of from to about 80% by weight of a five memberedunsaturated heterocyclic hydrocarbon compound and complementally from 95to about by weight of a saturated ether and a dissolved salt having theformulas MM'F MSCN or M010 where M is Li, Na, or K and M' is P, As orSb.

CROSS-REFERENCE TO RELATED APPLICATIONS This application is acontinuation-in-part of copending application Ser. No. 112,415 filedFeb. 3, 1971, now abandoned.

BACKGROUND OF THE INVENTION (1) Field of the invention This inventionrelates to high energy density batteries having active metal anodes,metallic compound cathodes and non-aqueous electrolytes.

(2) Prior art The art discloses a number of high energy density galvanicbatteries having voltaic cells consisting of light metal anodes,metallic compound cathodes and liquid non-aqueous electrolytes.

For example, French Pat. No. 1,490,726 to Societe des AccumulaleursFixes et de Traction (hereinafter S.A.F.T.) discloses such batteries inwhich the electrolyte is a saturated cyclic ether (tetrahydrofuran) andLiClO US. Patent No. 3,511,716 to Gabano et al., also assigned toS.A.F,T., teaches adding a second saturated ether to the tetrahydrofuranto increase solubility of the LiClO In US. Pat. No. 3,468,716, Eisenbergteaches an electrolyte composed of a mixture of a pentacyclic ester,saturated ether and LiClO None of the above teachings suggest the use ofunsaturated heterocyclics to improve the performance of a saturatedether/ salt electrolyte.

While the theoretical energy, i.e. the electrical energy potentiallyavailable from a selected anode-cathode couple, is easily calculated,there is a need to choose a nonaqueous electrolyte for such couple thatpermits the actual energy produced by the complete battery to approachthe theoretical energy to a practical degree. The problem is that it ispractically impossible to predict in advance how well a non-aqueouselectrolyte will function, in this respect, with a selected couple. Morebroadly stated, such batteries must be considered as whole units, eachunit having three parts which parts are not predictably interchangeablefrom unit to unit.

SUMMARY OF THE INVENTION This invention provides a novel high energydensity galvanic battery comprised of at least one voltaic cellcomprising an anode of a Group I-A or II-A metal having an equivalentweight no more than 23, a cathode containing a major proportion of metalcompound reducible by the anode and an electrolyte having a conductivityof at least 1 10- ohmcm. at 25 C., containing a solvent componentconsisting essentially of a mixture of from 5 to about by weight of atleast one five-memberedunsaturated heterocyclic hydrocarbon compoundhaving no replaceable hydrogen and having at least one heterocyclic atomselected from the group of oxygen, sulfur and nitrogen andcomplementally from to about 20% by weight of at least one saturatedether selected from the group of saturated ethers having the formulaRO(R'O) where R is a C to C alkyl group, R" is a C to 0,, alkyl group, Ris a 1,2-alkylene radical having 1 to 3 carbon atoms and n is 0 to 4 andthe formula RO(R'O),,R in which the saturated ether is a three tosix-membered ring where R-f-R" form an alkylene radical having from 2 to6 carbon atoms, R is a 1,1- or 1,2-alkylene radical having 1 to 3 carbonatoms and n=0 or 1 and a dissolved salt selected from the classconsisting of the compounds having the formulas MMF MSCN and MClO whereM is selected from the group consisting of Li, Na, and K and M isselected from the group consisting of P, As and Sb.

Such galvanic batteries show high utilization of the anode and cathodeactive ingredients and, generally, very low gas production duringdischarge. A particular advantage of the present invention is that itprovides an electrolyte which is highly effective in batterie withclose-spaced electrodes.

DESCRIPTION OF THE INVENTION The discussion of the battery and cellcomponents will be more easily understood with reference to the anode,electrolyte and cathode components.

Anodes The high energy density battery concept requires maximum batteryenergy output from a minimum weight and/ or volume of batterycomponents. Thus, the highly electropositive light metals of Groups I-Aand II-A of the Periodic Table are the most promising anode materials.Such metals having an equivalent weight no greater than 23 are used toavoid heavier metals with less available energy per unit weight. Byequivalent weight is meant the metal atomic weight divided by its usualmaximum oxidation valence. Therefore, lithium, sodium, beryllium,magnesium and calcium are possible anode metals. of these, lithium ispreferred, because it has the lowest equiv alent weight and is the mostelectropositive of all the metals. Lithium is also preferred because asa ductile, soft metal, it is easily disposed in a battery in intimateelectrical contact with a current collecting means providing an anodecontact external to the battery. Of course sodium shares this importantadvantage, but sodium is somewhat less preferred because it has about 3times the equivalent weight and almost twice the specific gravity.Sodium, is however, less costly than lithium.

Electrolytes The novel electrolytes of this invention are made up of asolvent component and, for conductivity, a salt dissolved in the solventcomponent. The solvent component consists essentially of at least twodiiierent non-aqueous solvents. One of these two different solvents is aS-membered, ring-oxygen, sulfur and/ or nitrogen unsaturatedheterocyclic hydrocarbon compound having no hydrogen replaceable by theabove active anode metals, for example, no labile hydrogen such asprovided by a OH, NH or SH group. By unsaturated is meant that in the 5-membered ring there is at least one carbon-carbon or carbon-nitrogendouble bond. Examples of such S-membered,

ring-unsaturated heterocyclic compounds include furans, l-alkylpyrroles,l-alkylpyrazoles, l-alkylimidazoles, thiazoles, isothiazoles, oxazoles,isoxazoles, furazans, oxadiazoles and their mixtures, wherein alkylgroups are usually lower alkyl groups, e.g. methyl or ethyl groups.

Representative are furan, 3-methylfuran, 3-ethylfuran,2,5-dimethylfuran, 3,4-dimethylfuran, l-methylpyrrole, l'ethylpyrrole,1,3-dimethylpyrrole, l-methylpyrazole, l-ethylpyrazole,1,3-dimethylpyrazole, l-methylimidazole, l-ethylimidazole,1,4-dimethylimidazole, thiazole, 2,4-dimethylthiazole, isothiazole,3,5-dimethylisoxazole, furazan, 3,4-dimethylfurazan, 1,2,4-oxadiazole,1,3,4-oxadiazole and the like and mixtures thereof.

Of the above unsaturated heterocyclic compounds 3,5- dimethylisoxazole,l-methylpyrrole, 3,4-dimethylfurazan, 2-methyl-4,S-dihydrooxazole,2,4-dimethylthiazole, furan and 2,5-dimethylfuran or mixtures thereofare preferred because of good miscibility with the ether cosolvents tobe described, efiectiveness in batteries when mixed with the ethercosolvents or ready availability. Especially preferred because they tendto provide a battery showing very low gassing are 3,5-dimethylisoxazole,l-methylpyrrole, furan, and 2,5-dimethylfuran and 2-methyl-4,5-dihydrooxazole.

Normally for the solvent component of the electrolyte one utilizes from5 to about 80% by weight of one or more of the above unsaturatedheterocyclic compounds and, complementally from 95 to about 20% byweight of at least one saturated ether having the formula RO(RO),,R"where R and R" are C, to C alkyl groups, n is to 4 and R is a C to C1,2-a1kylene group, or alternatively, where the saturated ether is a 3to 6-membered rnig, viz where R and R" taken together form a C to Calkylene radical, R is a C to C 1,1- or 1,2- alkylene and n is 0 to l.Representatve of such saturated ethers are, for example, dimethyl ether,diethyl ether, methylpropyl ether, ethylbutyl ether,1,2-dimethoxyethane, 1,2-dibutoxypropane, the dimethyl ethers ofdiethylene glycol, triethylene glycol and tetraethylene glycol,tetrahydrofuran, dioxolane, 1,3-propylene oxide, 1,2- propylene oxide,2,3-butylene oxide, 3-ethyltetrahydrofuran, 1,4-dioxane,3-methyldioxane-l,4, tetrahydropyran, 4-methyltetrahydropyran,4,4-dimethyldioxane-1,3, 4-methyldioxane-1,3, 2-ethyldioxolane, mixturesthereof and the like. Among these, diethyl ether, tetrahydrofuran, and1,2-dimethoxyethane or mixtures thereof are preferred because ofeffectiveness in batteries, good miscibility with the above preferredunsaturated heterocyclic compounds and/or ready availability or lowcost.

It should be understood that appreciable amounts of organic diluents canbe present in the solvent component of the electrolyte without departingfrom the concept of this invention. It is essential that there bepresent at least about 5% by weight of one of the S-membered unsaturatedheterocyclics and at least 20% by weight of one of the saturated ethers,and preferably a major amount of the electrolyte solvent is composed ofmembers of these two classes. However, diluents which do not appreciablyinterfere with the function of the two required classes of compounds canbe present in substantial amounts and can contribute even up to 40% or50% by weight of the solvent. Representative of such diluents are methylacetate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate,propylene carbonate, propyl acetate, ethylene carbonate, toluene and thelike.

Salts useful for providing conductivity to the abovedescribed solventcomponent are those having the formulas MMF MSCN and MClO, where M isthe cation of -Li, Na or K, and M is P, As or Sb. Representative of suchsalts are, for example, LiPF NaPF KPF NaAsF KAsF LiSbF LiSCN, NaSCN,LiClO KCIO Of these salts LiClO NaPF and LiCNS are preferred because ofeffectiveness in providing high conductivity and inertness towards theanode metals and the solvents.

The concentration of said salts in said solvents can range up tosaturation. Normally a suflicient quantity of such salt is dissolved inthe solvent to provide an electrolyte having a conductivity of at least1 10- ohm" cmr Preferred concentrations of the preferred salts usuallylie between about 5 and about 30% by weight of the whole electrolyte.Within this range high conductivity is provided. It is most preferredthat the electrolyte salt used is LiClO in amounts of from about 10% toabout 15% based on the weight of electrolyte; NaPF in amounts of about20% based on the weight of electrolyte; or LiSCN in amounts of about 10%based on the weight of electrolyte.

Cathodes Broadly the cathodes of the present invention contain a majorproportion of a compatible metal compound reducible by the anode metals,said metal compound being in practical electrical contact with a currentcollecting means ultimately providing an external electrical cathodecontact for the battery. By compatible is meant such reducible metalcompound which is practically resistant to attack on the non-aqueouselectrolyte or, through dissolution in said electrolyte, to attack onthe active anode metal.

Operable reducible metal compounds include inorganic metal compounds,for example, simple halides, oxides or sulfides of such metals as lead,palladium, mercury, cadminum, silver, copper, nickel, iron andmanganese. Representative are, for example, 'PbOg, HgO, Hg O, OdFg, Ag0, AgCl, CuO, Cu 0, CuS, Cu S, Cu S (digenite), NiS, Ni S -FeO, Fe OFeS, FeS,, Fe O MnO mixtures thereof and the like. Other suitablecathodes include the phosphates, sulfates and chromates of metals suchas iron, copper, nickel, silver, vanadium and tungsten and the oxides,fluorides and sulfides of vanadium and tungsten. Representative of theseare V 0 Ag P0 CuSO, Ag Cr0 and W0 More complex inorganic metal compoundscan also be utilized as cathode materials. Among these are, for example,Cu Fe(CN) and CuCO .Cu(OH) Organic acid salts are also useful.Representative, for example, are nickel oxalate, copper tartrate andcopper citrate. Such non-metallic compounds as the carbon fluoridedisclosed in U.S. Pat. 3,536,532 are also suitable cathodes.

Cathodes may be prepared from such reducible metal compounds by a widevariety of art known means such as, for example, pressing the compoundsin finely divided form into a coherent body which can be operably placedin a battery in contact with the current collecting means, or castingthose fusible members of the above group, etc. It will be appreciatedthat, since many such reducible metal compounds are not conductive theymust be mixed with a suitably conductive material, such as up to 15% byweight of carbon, before being formed into cathodes.

Preferred metal compounds are conductive and require little or no addedconductive material. Such preferred reducible metal compounds are thoseconsisting essentially of CuS, FeS, Niqss and NiS. CuS is particularlypreferred because of its inertness and high performance. These metalsulfides are available commercially or easily prepared, for example, byprecipitation by contacting an aqueous solution of the appropriate metalion with a sulfide ion source and, as discussed more fully below, bysintering a mixture of the elements, viz the appropriate metal or amixture of the metals in particulate form with particulate elementalsulfur. Since as already stated these sulfides are conductive they maybe formed into cathodes without added conductive material. However,mixing such compounds with a small amount, e.g. 5% or less, of aparticulate conductive material prior to final forming may improve theperformance of the cathode in terms of high active ingredientutilization during battery discharge.

Cathodes of these preferred sulfides are readily formed by simple means.For example, iron sulfide cathodes consisting essentially of FeS, i.e.having greater than 70% FeS and some iron oxide are prepared by pressinga mixture of iron and sulfur powders (1:1 atom ratio) into a coherentstructure and sintering the structure at 600-65 C. for to 30 minutes.Highly preferred copper sulfide cathodes consisting essentially of CuS,i.e. containing more than 90% CuS, are very readily prepared from amixture of copper and sulfur powders pressed into a desired shape andcured at above the melting point of sulfur, such as in Exainple 1. NiSand Ni S suitable for pressing into cathodes are prepared by sinteringin an inert atmosphere, a 1:1 atom ratio mixture of nickel and sulfurpowders at about 600 C., grinding the resulting products and thenpressing the pulverized material into a cathode of desired shape. X-raydilfraction analyses indicate that Ni-,S is the major product with shortperiods of such sintering, e.g. up to 2.5 hours, while MS is the majorproduct of longer sintering, e.g. 16 hours. Thus choice of sinteringmethod provides materials'consisting essentially of Ni S, or NiS.

A further method for preparing rigid, coherent iron or nickel sulfidecathodes for use in the batteries of this invention comprises mixing alittle free sulfur, e.g. about 10 to about with particulate iron sulfideor nickel sulfide, pressing the mixture to form a coherent body and thenheating the body slowly to about 350 C. or higher and maintaining thebody at that temperature to vaporize away any free sulfur. This processprovides a cathode selfbondedby solid solutions of the original metalsulfide and the sulfur. Such solid solutions provide little or no freesulfur which may interfere with high battery performance.

In some instances it is desirable to incorporate into the 6 In a dryargon atmosphere, the recess in a matching plate was packed with 0.19 g.of lithium metal. A gas-tight cell was prepared in the argon atmosphereby bolting the two plates together with insulated bolts against a 0.4mm. thick, circular pad of inert, non-woven fiber held inside apolypropylene spacer ring of somewhat larger diameter than the cathodeand anode recesses. A tight seal between the edges of the spacer and thenickel plates was assured by using synthetic chlorinated rubber gaskets.There resulted a cell with anode and cathode faces closely spaced, 0.4mm. apart. The cell was evacuated and allowed to fill, until thepressure was at atmospheric pressure, with an electrolyte solution whichwas 12 weight percent of LiClO 73 weight percent of tetrahydrofuran and15 weight percent of 3,5-dimethylisoxazole. After sealing the openingsin the plates used to evacuate and to fill the cell, the cell wasdischarged at room temperature (about 25 C.) through a constant load of180 ohms to an arbitrary cut-01f of 1.0 volt. The average dischargevoltage was 1.52 volts. Cathode utilization, calculated as CuS was 80%and the battery delivered 722 watt-hours per kg. of lithium and coppersulfide as calculated from the total amount of lithium and coppersulfide originally present in the battery. This battery produced nomeasurable volume of gas.

\ Examples 2-7 TABLE I Discharge CuS Watt-hr. Gas vol. pe ExampleUnsaturated heterocycllc solvent LlClOi, load, utilization, per kg.interna 0. (wt. percent) wt. percent ohms percent Li-CuS cell vol.

cathode structure some binder material. Ordinarily such a binder isincorporated as a powder prior to fabrication of the cathode andrepresentative of suitable resin binders is polytetrafluoroethylenepowders in amounts ranging from about 1% to about 15% by weight.

Batteries This invention does not concern battery design orconstruction; nor is electrode spacing meant to be limited. However, itis desirable to utilize batteries having closely spaced electrodes, sayspacings of from about 0.2 to about 0.5 mm., to minimize electrolytequantity and battery size.

The electrolytes of this invention would be readily utilized in aclose-spaced electrode battery such as that suggested by the disclosureof Gabano et al. in US. 3,511,716.

EXAMPLES Example 1 A mixture having a 1:1 atom ratio of sulfur-to-copperwas prepared from sublimed sulfur powder and electrolytic copper dusthaving 50,u maximum particle size. The mixture was aged at about 25 C.for a period of about 7 days. By means of a powder press, a coherentdisk of the aged mixture was prepared in contact with a coextensive diskof nickel metal mesh. The coherent disk was next cured for about 4minutes by heating between two nickel plates previously heated to 225 C.The resulting flat cathode structure contained 0.96 g. of copper sulfideand had a single face area of 6.5 cmF.

'Next the cathode disk was tightly fitted, mesh-side-tonickel, into acylindrical machined recess in a nickel plate.

Surprisingly, as little as 5% of one of the invention unsaturatedheterocyclics in the electrolyte strikingly improves battery performancevis a vis that of a battery having none of such heterocyclic.

The following comparative example illustrates the superiority in cathodeutilization and energy output of the example batteries over a Li/CuSbattery containing a saturated ether based electrolyte as taught inFrench Pat. No. 1,490,726.

Example 8 A battery assembled as in Example 1 and discharged through 174ohms had an electrolyte of 20 weight percent NaPF 56 weight percent3,5-dimethylisoxazole and 24 weight percent 1,2-dimethoxyethane. Thebattery showed 84% 018 utilization, produced 692 watt-hours per kg. ofLi and CuS. No gas was produced by the battery.

The following comparative example indicates that the unsaturatedheterocyclic compounds of the invention used without a saturated etherare inefiective.

7 Example 10 A battery as in Example 9 but having an electrolyte of 20weight percent of NaPF and 80 weight percent of 3,5-dimethylisoxazole,showed only 4% Gus utilization and delivered only about 2 watt-hours perkg. of Li and CuS.

The following comparative example indicates further that the saturatedethers of the invention used without the unsaturated heterocycliccompound are poor electrolytes in the present batteries.

Example 11 A battery as in Example 9 with 20 weight percent of NaPFdissolved in 80 weight percent of 1,2-dimethoxyethane showed only 3% Gusutilization and delivered only about 24 watt-hours per kg. of Li andCuS.

The following example illustrates the use of a mixture of saturatedether components and yet another salt of the invention.

Example 12 A battery as in Example 1 discharged through 180 ohmscontained 9.0 weight percent of lithium thiocyanate, 27.6 weight percentof tetrahydrofuran, 45.4 weight percent of 3,5-dimethylisoxazole and 18weight percent of the dimethyl ether of diethylene glycol. CuSutilization was 90%. The battery produced 658 watt hours per kg. of Liand CuS. No gas was produced.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In a high energy density galvanic battery comprising at least onevoltaic cell comprising an anode of a Group I-A or IIA metal having anequivalent weight no greater than 23, an electrolyte solution and acathode containing a major proportion of metal compound reducible bysaid anode, the improvement comprising using as the electrolyte solutionan electrolyte having a conductivity at 25 C. of at least 1x10- ohmcm.-containing a solvent component consisting essentially of a mixture offrom 5 to about 80% by weight of at least one five-membered unsaturatedheterocyclic hydrocarbon compound having no replaceable hydrogen andhaving at least one heterocyclic atom selected from the group of oxygen,sulfur and nitrogen and complementally from 95 to about 20% by weight ofat least one saturated ether selected from the group of saturated ethershaving the formula R0 (RO),,R" where R is a C to C alkyl group, R" is aC to C alkyl group, R' is a 1,2-a1kylene radical having 1 to 3 carbonatoms and n is 0 to 4 and the formula R0 (R'O) R" in which the saturatedether is a three to six-membcred ring where R+R" form an alkyleneradical having from 2 to 6 carbon atoms, R is a 1,1- or 1,2-alkyleneradical having 1 to 3 carbon atoms and m==0 or 1 and a dissolved saltselected from the class consisting of the compounds having the formulasMMF, MCNS and MClO where M is Li, Na or K and M is P, As or Sb.

2. The improved battery of claim 1 wherein the unsaturated heterocycliccompound is selected from furans,

l-alkylpyrroles, l-alkylpyrazoles, 1-alkylimidazoles,.thiazoles,isothiazoles, oxazoles, isoxazoles, furazans, oxadiazoles and theirmixtures.

3. The improved battery of claim 1 in which the anode is selected fromthe group consisting of lithium and sodium, the cathode consistsessentially of metallic compound selected from the group consisting ofCuS, FeS, NiS and N iS and the electrolyte solvent consists essentiallyof at least one unsaturated heterocyclic selected from3,5-dimethylisoxazole, l-methylpyrrole, 3,4-dimcthylfurazan,2-methyl-4,5-dihydrooxazole, 2,4-dimethylthiazole, furan and2,5-dimethylfuran, and at least one saturated ether selected fromdiethyl ether, 1,2-dimethoxyethane, the dimethyl ether of diethyleneglycol and tetrahydrofuran and the dissolved salt is LiClO NaPF or LiSCNin amounts ranging from about 5% to about 30% based on the weight ofelectrolyte.

4. The improved battery of claim 3 in which the anode is lithium and thecathode consists essentially of CuS.

5. The improved battery of claim 3 in which the unsaturated heterocyclicsolvent component is 3,5.-dimethylisoxazole, l-methylpyrrole, furan,2,5-dimethylfuran or 2-methyl-4,5-dihydrooxazole and the saturated ethercomponent is 1,2-dimethoxyethane or tetrahydrofuran.

6. The improved battery of claim 5 in which the anode is lithium and thecathode consist essentially of CuS.

7. The improved battery of claim 3 in which the electrolyte consistsessentially of from about 10 to about 15% by weight of LiClO from about5 to about 50% by weight of an unsaturated heterocyclic compoundselected from 3,5-dimethylisoxazole, l-methylpyrrole, 2-methyl-4,S-dihydrooxaZole, 2,4dimethylthiazole, furan and2,5-dimethylfuran and the balance of the weight percent of theelectrolyte being tetrahydrofuran.

8. The improved battery of claim 6 in which the electrolyte consistsessentially of about 20% by weight of NaPF about 55% by weight of3,5-dimethylisoxazole and about 25% by weight of 1,2-dimethoxyethane.

9. The improved battery of claim 6 in which the electrolyte consistsessentially of about 10% by weight of LiSCN, about 45% by weight of3,5-dimethylisoxazole, about 30% weight of tetrahydrofuran and about 15%by weight of the dimethyl ether of diethylene glycol.

References Cited v STATES PATENTS,

